Field of the Invention
The present invention relates to a glass substrate for a magnetic disk to be a source of a magnetic disk for heat assisted magnetic recording and a magnetic disk for heat assisted magnetic recording.
Background Information
Conventionally, a glass substrates is suitably used for a magnetic disk which is used as one of information recording mediums. Today, in response to the request for increased recording capacity of a hard disk drive (HDD) device, the density of magnetic recording is being increased. Consequently, a magnetic recording information area is micronized by making a flying height of a magnetic head from a magnetic recording surface extremely low. Dimension and form of the glass substrate used for such a magnetic disk are preferably made with high accuracy with respect to a target value.
Especially, the lower a flying height of a magnetic head from a magnetic recording surface becomes, the more scratches on the principal face of a magnetic disk can occur when the magnetic head is in operation, caused by a fine waviness on the principal face of the magnetic disk. Accordingly, it is preferable that the level of the fine waviness on the principal face of a glass substrate for a magnetic disk to be a source of a magnetic disk is decreased.
On the other hand, recently, the heat assisted magnetic recording (HAMR) system is noticed as a technology which further increases the recording capacity. A magnetic disk for heat assisted magnetic recording is obtained by forming at least an adhesive layer, an underlying layer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricant layer on the principal face of a glass substrate for a magnetic disk. As a forming method of a magnetic layer, a method of performing a heat treatment to a glass substrate for a magnetic disk at a temperature close to a glass transition temperature Tg is known (JP 2013-178855 A).